1. Field of the Invention
This invention relates to bed and chair coverlets, pads, and covers for preventing, reducing, and treating decubitus ulcers, known as pressure sores and bed sores, by providing a low friction surface against a patient's skin, by absorbing vapor and moisture coming from the patient, and by circulating an amount of air beyond normal ambient air convection to keep wounds dry, to promote healing, and to regulate body temperature.
2. Description of Related Art
It is well known that patients that stay in bed or chairs for extended periods of time can develop decubitus ulcers, pressure sores, or bed sores. The ulcers are often caused by the reduction of blood flow to soft tissues that are compressed by the weight of the patient between the bed or chair surface and bony prominences of the patient. The continued lack of blood flow, and resultant lack of oxygen, cause cells to die and eventually cause the ulcers. The time-frame for occurrence of these ulcers depends on various factors such as the firmness and friction of the surface against the patient's skin, temperature, moisture, and the health and susceptibility of the skin due to age or illness.
To allow blood to flow to the areas of restriction, the patients are often turned regularly by nursing or hospital personnel to reduce the occurrence of the ulcers. Turning of the patients is not always possible, especially if the patient is not in a facility that provides such services.
Alternately, attempts have been made to reduce the occurrence of decubitus ulcers by mattresses or pads that are intended to more evenly redistribute the pressure under bony prominences. Redistribution of skin pressure is accomplished by static support surfaces such as foam mattresses and air or water mattresses and the like, and by alternating pressure inflatable mattresses that dynamically shift the location of support pressure under the patient. The alternating pressure mattresses can have a series of side-by-side inflatable air chambers or cells that are alternately inflated and deflated in a manner that shifts the support location under the patient to and from adjacent air chambers. An example of an alternating pressure inflatable support surface is illustrated in U.S. Pat. No. 5,509,155, the disclosure of which is incorporated herein by reference.
The alternating pressure inflatable support surfaces can also include an additional feature to help heal the skin after breakdown or to help in the prevention of skin breakdown. The feature is called "low air loss", and the purpose is to circulate a low amount of air, beyond normal air convection, to remove moist air vapor given off by the patient, to keep wounds dry and to promote healing.
Until now, there were essentially two approaches to providing a low air loss feature, with both approaches resulting in "low air loss mattresses". Low air loss mattresses are alternating support pressure inflatable mattresses that include a low air loss feature as an integral part of the mattress. The patient normally lies on a vapor permeable coverlet on top of the low air loss mattress. The low air loss feature circulates air below the coverlet to dry moisture coming from the patient and passing through the coverlet to the space between the coverlet and the mattress.
The two approaches heretofore available for providing a low air loss feature are:
First, tiny holes are provided in the top surface of the inflatable air cells. The tiny holes allow extra air to circulate between the air cell array and the coverlet on which the patient lies to evaporate vapor moisture.
Second, an air tube is run from the air pump to the air cell enclosure, but exterior to the alternating pressure air cells themselves. The additional air tube blows excess air in the same manner as holes in the air cells. However, some sort of diffuser sheet is normally required to somewhat evenly spread the air throughout the space below the patient.
There are several disadvantages with these approaches of providing low air loss. For the first approach, a large compressor pump must be used to have sufficient volume of air to inflate the air cells, and to keep up with the demand of continually loosing air through the holes provided in the air cells that are trying to be inflated. Large compressor pumps tend to be noisy and have high electrical consumption. The second approach includes the same problem.
In both approaches the amount of moisture removed is only that which comes through the vapor permeable coverlet on which the patient is lying. Generally, no air actually reaches the patient to remove excess moisture on the wounds or from the skin surface.
Primarily in the first approach, there is a trade off on how many holes can be provided in the air cells and the volume of the pump and its ability to keep up with the demand. The typical system has only a few holes on about 50% of the air cells, allowing for low or poor air distribution. If more holes are punched in the air cells directly under the patient, these air cells will loose air faster, with the patient tending to bottom out on the bed.
In both these approaches, as stated above, no air reaches the patient directly. The patient lies on a waterproof yet vapor permeable coverlet, which does not allow air to blow through the coverlet. Air flowing directly to the patient's skin drys wounds and promotes healing.
Some systems have the patient lying on a loose woven material, that is not waterproof, and also happens to have a less smooth surface causing shear on the patient's skin. The loose woven material allows air to pass through, but looses the other characteristics of waterproof yet vapor permeable material, including patient comfort. If the patient were to lie directly on the mattress, the patient would at least partially clog the tiny holes in the air cells preventing the low air loss feature. Also, the moist vapor given off by the patient could not pass through the vapor barrier material of the air cells resulting in a sweaty and uncomfortable patient.
With both of the above approaches, the low air loss option cannot be turned on or off independently of the air flow to the mattress. If the low air loss therapy is not desired, a different system must be utilized with another controller and a different air cell array.
Examples of low air loss mattresses, that include the above mentioned disadvantages, are disclosed in U.S. Pat. Nos. 4,267,611; 4,653,130; and 5,375,273. The '611 and '273 patents discloses utilizing small holes directly in the air chambers or air cells of alternating pressure inflatable mattresses to provide escaping air between the mattress and the patient. The '273 patent additionally discloses utilizing a vapor-permeable sheet between the low air loss mattress and the patient. The escaping air flows between the mattress and the vapor-permeable sheet and not directly onto the patient. See the '273 patent at col. 1, lines 54-66.
The '130 patent discloses an alternating pressure inflatable mattress having an air cell array with tiny holes therein to provide escaping air to the patient, and which is separate from the alternating pressure inflatable cells used for patient support. The '130 patent is an example of the second approach described herein above.
The present invention provides a totally new device to provide a low air loss feature by providing a low air loss coverlet.